1. Field of the Invention
This invention relates to a process for the production of hydrolyzed vegetable proteins, containing no detectable levels of monochlorodihydroxypropanol. The resultant hydrolyzed vegetable protein is clean and bland in flavor and exhibits substantial flavor enhancement characteristics.
2. Description of the Prior Art
The preparation of conventional hydrolyzed vegetable proteins (HVPs) is generally carried out by acid hydrolysis with hydrochloric acid under refluxing conditions, specifically using 6M hydrochloric acid at 109.degree. C. and atmospheric pressure. It has been demonstrated that hydrolyzing vegetable proteins at these conditions results in the chlorination of glycerol, which is derived from the residual fatty substances present in the crude protein, to produce monochlorodihydroxypropanols (MCDPs) and dichloropropanols (DCPs). As MCDPs and DCPs exhibit questionable properties and characteristics, their presence is not desired in food products. DCPs are readily removed during the evaporation or concentration steps of standard processes. Unfortunately, MCDPs are not removed, but are concentrated in the finished product, and therefore, additional processing steps must be taken to remove the MCDPs from the finished product.
In a conventional acid hydrolysis process for preparing HVPs, the formation of MCDPs and DCPs can be avoided by using sulfuric or phosphoric acid in place of hydrochloric acid. However, the HVPs produced by hydrolyzing with sulfuric or phosphoric acid are of an inferior quality in that they exhibit a bitter flavor.
The specific problem is that MCDP is derived during conventional acid hydrolysis from the chlorination of the glycerol derived from the residual fatty substances which are present in crude proteins. As an example, vital wheat gluten which is approximately 75% protein, also contains 5.0 to 9.5% fat and other lipid materials, is an abundant source of glycerol in the form of a complex mixture of mono-, di- and tri-glycerides, phospholipids and glycolipids. Numerous factors which are believed to effect the formation of MCDP include the presence of high concentrations of chloride ions, high amounts of excess acid, high refluxing temperatures and long reaction times. It is thought that the bound glycerol is more active in forming MCDPs than unbound glycerol.
Much is also known about the use of enzymes to hydrolyze vegetable proteins for food use, but not for the purpose of flavor enhancement. What is taught in the existing art is generally directed toward producing functionally improved proteins, such as eliminating bitter peptide formation during enzyme hydrolysis as shown in U.S. Pat. No. 4,636,388. Specifically, the patent discloses a low ash protein product which is particularly adapted for enzymatic hydrolysis. A dispersion of protein is gelled and then washed in particulate form in a liquid in order to allow a portion of the non-proteinaceous material to defuse from the gel into the liquid, and then the liquid is separated from the gel. The pretreated product is then hydrolyzed enzymatically, preferably with fungal protease and pancreatin.
U.S. Pat. No. 4,757,007, discloses and claims a process for the preparation of hydrolyzed products of soy protein by partially hydrolyzing soy protein with protease, and then separating the resulting hydrolyzed products by using a 5% aqueous solution of trichloroacetic acid. The portion of hydrolyzed protein with low solubility possesses excellent emulsifying properties, while the one with high solubility possesses excellent foaming properties.
In U.S. Pat. No. 3,830,942, a soluble protein product is produced which is particularly useful in highly acidic foods, and an insoluble protein product is prepared which is used in preparing protein enriched bakery goods. The patent discloses the method for producing the two products by forming an aqueous solution of defatted oleaginous seed materials, adjusting the pH of the slurry to the isoelectric point of the seed materials, heating the slurry to elevated temperatures, adding an enzyme to the slurry, agitating the mixture during hydrolysis of the material and thereafter, separating the hydrolyzed and unhydrolyzed portions of the protein product.
In U.S. Pat. No. 4,665,158 to Armamet et al., a process is disclosed for hydrolyzing dehydrated protein materials with gaseous hydrochloric acid. Partial hydrolysis is achieved by the process when a protein material is impregnated with hydrochloric acid and left to rest at a selected temperature until the desired degree of hydrolysis is obtained. If complete hydrolysis is desired, then the protein-hydrochloric acid combination is subjected to heat under pressure in an autoclave.
Although enzyme hydrolysis and acid hydrolysis are generally separate procedures, one reference has been found which discloses the combination of acid and enzyme hydrolysis to obtain a protein hydrolyzate. In USSR Patent Application No. 442800, a method of obtaining a preparation for parenteral protein feeding is taught. A method is disclosed wherein the raw protein material undergoes enzymatic cleavage, followed by acid hydrolysis with 5.0% sulfuric acid (4.0N), in a carbon dioxide atmosphere. Thereafter, the hydrolyzate is passed through an anion exchange column, treated with aluminum hydroxide and passed through a column containing cation exchange resin. The acid hydrolysis takes place at about 100.degree. C. for about seven (7) hours.
Many attempts have been made over the years to produce hydrolyzed vegetable protein products which are used for various purposes, however, to date no process has been taught which produces a hydrolyzed vegetable protein with reduced or non-existent levels of MCDP or DCP due to preventing MCDP and DCP production by controlling the parameters of the acid hydrolysis, and which exhibits substantial flavor enhancement characteristics.